Probes for imaging huntingtin protein

1. An imaging agent comprising a compound of Formula (I),

or a pharmaceutically acceptable salt thereof, wherein

L 1 is absent;

R 1 is

optionally substituted with one, two, or three C 1 -C 6 alkoxy;

L 2 is —N(R 4 )—;

R 2 is chosen from

hydrogen,

C 1 -C 6 alkyl, and

C 1 -C 6 alkyl substituted with C 1 -C 6 alkoxy, amino, (alkyl)amino, (dialkyl)amino, or hydroxy;

one R 3 is cyano, and an optional additional R 3 is independently selected from

halo,

cyano,

C 1 -C 6 alkoxy,

C 1 -C 6 alkyl substituted with amino, (alkyl)amino, or di(alkyl)amino, and ethynyl optionally substituted with tri(alkyl)silyl;

R 4 is chosen from hydrogen and C 1 -C 6 alkyl; and

m is 1 or 2,

wherein the compound of Formula (I), or a pharmaceutically acceptable salt thereof, is labeled with one or more positron-emitting radionuclides.

2. The imaging agent of claim 1 ,

wherein R 1 is substituted with methoxy.

3. The imaging agent of claim 1 ,

wherein R 1 is

4. The imaging agent of claim 1 , wherein R 4 is hydrogen or methyl.

5. The imaging agent of claim 1 , wherein R 2 is chosen from hydrogen, methyl, 2-methoxyethyl, 2-hydroxyethyl, and 2-(dimethylamino)ethyl.

6. The imaging agent of claim 1 , wherein m is 1 and R 3 is cyano.

7. The imaging agent of claim 6 , wherein m is 2 and an additional R 3 is chosen from bromo, chloro, fluoro, aminomethyl, 2-(trimethylsilyl)ethynyl, ethynyl, methoxy, and cyano.

8. The imaging agent of claim 7 , wherein the additional R 3 is chosen from bromo, chloro, fluoro, methoxy, and cyano.

9. The imaging agent of claim 8 , wherein the additional R 3 is cyano.

10. An imaging agent comprising a compound chosen from:

2-(5-fluoro-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

6-fluoro-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

7-fluoro-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

2-(5-methoxy-1-benzofuran-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-[6-fluoro-3-(methylamino)imidazo[1,2-c]pyridin-2-yl]-1-benzofuran-5-ol;

2-(5-methoxy-1-benzofuran-2-yl)-N-(2-methoxyethyl)imidazo[1,2-c]pyridin-3-amine;

2-[7-fluoro-3-(methylamino)imidazo[1,2-c]pyridin-2-yl]-1-benzofuran-5-ol;

2-{3-[(2-hydroxyethyl)amino]imidazo[1,2-c]pyridin-2-yl}-1-benzofuran-5-ol;

2-(5-hydroxy-1-benzofuran-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-[5-(2-fluoroethoxy)-1-benzofuran-2-yl]-3-(methylamino)imidazo[ 1,2-c]pyridine-7-carbonitrile;

2-(4-methoxyphenyl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(6-methoxy-1-benzofuran-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

7-methoxy-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[ 1,2-c]pyridin-3-amine;

3-(methylamino)-2-[3-(pyridin-3-ylmethoxy)phenyl]imidazo[1,2-c]pyridine-7-carbonitrile;

3-(methylamino)-2-[4-(pyridin-3-ylmethoxy)phenyl]imidazo[1,2-c]pyridine-7-carbonitrile;

7-chloro-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

7-bromo-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

2-(5-methoxy-1-benzofuran-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-6-carbonitrile;

2-(5-bromo-1-benzofuran-2-yl)-3-(methylamino)imidazo[ 1,2-c]pyridine-7-carbonitrile;

3-(methylamino)-2-[3-(pyrazin-2-yl)phenyl]imidazo[1,2-c]pyridine-7-carbonitrile;

3-(methylamino)-2-[4-(pyrazin-2-yl)phenyl]imidazo[1,2-c]pyridine-7-carbonitrile;

2-[(E)-2-(4-methoxyphenyl)ethenyl]-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-methoxy-1-benzofuran-2-yl)-3-[(2-methoxyethyl)amino]imidazo[1,2-c]pyridine-7-carbonitrile;

2-(2,3-dihydro-1,4-benzodioxin-6-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-bromofuran-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(4-cyanophenyl)-3-(methylamino)imidazo[ 1,2-c]pyridine-7-carbonitrile;

2-(1-benzofuran-5-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

3-(methylamino)-2-[4-(prop-2-yn-1-yloxy)phenyl]imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-fluoro-1-benzofuran-2-yl)-3-(methylamino)imidazo[ 1,2-c]pyridine-7-carbonitrile;

2-{3-[(5-methoxypyrazin-2-yl)methoxy]phenyl}-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-{5-[(5-methoxypyrazin-2-yl)methoxy]pyridin-2-yl}-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

3-(dimethylamino)-2-(5-methoxy-1-benzofuran-2-yl)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-methoxy-1-methyl-1H-1,3-benzodiazol-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(6-methoxy-1,3-benzothiazol-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-methoxy-1,3-benzoxazol-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-methoxy-1H-1,3-benzodiazol-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-methoxy-1-benzofuran-2-yl)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(6-methoxy-1-methyl-1H-1,3-benzodiazol-2-yl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

3-(methylamino)-2-[5-(pyridin-3-ylmethoxy)-1-benzofuran-2-yl]imidazo[1,2-c]pyridine-7-carbonitrile;

3-amino-2-[5-(2-fluoroethoxy)-1-benzofuran-2-yl]imidazo[1,2-c]pyridine-7-carbonitrile;

3-amino-2-(5-methoxy-1-benzofuran-2-yl)imidazo[1,2-c]pyridine-7-carbonitrile;

2-(5-methoxy-1-benzofuran-2-yl)-3-(methoxymethyl)imidazo[1,2-c]pyridine-7-carbonitrile;

3-[(dimethylamino)methyl]-2-(5-methoxy-1-benzofuran-2-yl)imidazo[1,2-c]pyridine-7-carbonitrile;

2-{5-[2-(dimethylamino)ethoxy]-1-benzofuran-2-yl}-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

3-(methylamino)-2-{4-[(pyridin-3-ylmethoxy)methyl]phenyl}imidazo[1,2-c]pyridine-7-carbonitrile;

3-{[2-(dimethylamino)ethyl]amino}-2-(5-methoxy-1-benzofuran-2-yl)imidazo[1,2-c]pyridine-7-carbonitrile

tert-butyl 2-[7-cyano-3-(methylamino)imidazo[1,2-c]pyridin-2-yl]-4H,5H,6H,7H-furo[3,2-c]pyridine-5-carboxylate;

7-(aminomethyl)-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

3-(methylamino)-2-{3-[(pyridin-3-ylmethoxy)methyl]phenyl}imidazo[1,2-c]pyridine-7-carbonitrile;

2-{4-[(5-methoxypyrazin-2-yl)methoxy]phenyl}-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-{6-[(5-methoxypyrazin-2-yl)methoxy]pyridin-3-yl}-3-(methylamino)imidazo[1,2-a]pyridine-7-carbonitrile;

2-(5-methoxy-1-benzofuran-2-yl)-N-methyl-7-[2-(trimethylsilyl)ethynyl]imidazo[1,2-a]pyridin-3-amine;

7-ethynyl-2-(5-methoxy-1-benzofuran-2-yl)-N-methylimidazo[1,2-c]pyridin-3-amine;

2-(4-{[(5-methoxypyridin-2-yl)methyl]amino}phenyl)-3-(methylamino)imidazo[1,2-a]pyridine-7-carbonitrile;

2-(4-{5H,6H-imidazo[2,1-b][1,3]thiazol-3-ylmethoxy}phenyl)-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-{10-methoxy-7-thia-2,5-diazatricyclo[6.4.0.0 2,6 ]dodeca-1(12),3,5,8,10-pentaen-4-yl}-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile;

2-{11-methoxy-7-thia-2,5-diazatricyclo[6.4.0.0 2,6 ]dodeca-1(12),3,5,8,10-pentaen-4-yl}-3-(methylamino)imidazo[1,2-c]pyridine-7-carbonitrile; and

2-{5-[(5-methoxypyridin-2-yl)methoxy]pyrazin-2-yl}-3-(methylamino)imidazo[1,2-a]pyridine-7-carbonitrile;

or a pharmaceutically acceptable salt thereof, and wherein the compound is labeled with one or more positron-emitting radionuclides.

11. The imaging agent of claim 1 , wherein said agent contains one or more positron-emitting radionuclides selected from: 11 C, 13 N, 15 O, and 18 F.

12. A method of generating diagnostic images in an individual comprising administering an effective amount of an imaging agent of claim 1 to an individual, and generating an image of at least a part of said individual.

13. The method of claim 12 , wherein generating an image of at least a part of said individual comprises generating an image to detect the presence or absence of huntingtin protein (HTT protein) monomers or aggregates in the brain of said individual; and detecting the presence or absence of a pathologic process.

14. The method of claim 13 , wherein said HTT protein monomers or aggregates are present in the basal ganglia of said brain of said individual.

15. The method of claim 13 , wherein the pathologic process is a neurodegenerative disease.

16. The method of claim 15 , wherein the neurodegenerative disease is chosen from Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease, Prion disease and spinocerebellar ataxias.

17. The method of claim 16 , wherein the neurodegenerative disease is Huntington's disease (HD).

18. The method of claim 12 , wherein said effective amount of said imaging agent comprises from about 0.1 to about 20 mCi.

19. The method of claim 18 , wherein said effective amount of said imaging agent comprises about 10 mCi.

20. The method of claim 12 , wherein said generating an image comprises positron emission tomography (PET) imaging, PET with concurrent computed tomography imaging (PET/CT), PET with concurrent magnetic resonance imaging (PET/MRI), or a combination thereof.

21. The method of claim 20 , wherein said generating an image comprises PET imaging.